An international team of scientists, including Dr Luca Sapienza from the University of Southampton, have developed a new technique for finding quantum dots.
A quantum dot should produce one and only one photon—the smallest constituent of light—each time it is energized, and this characteristic makes it attractive for use in various quantum technologies, such as secure communications. However, the trick is in finding them.
While they appear randomly, in order for the dots to be useful they need to be located in a precise relation to some other photonic structure, be it a grating, resonator or waveguide, which will enable control of the photons that the quantum dot generates. However, finding the quantum dots—they’re just about 10 nanometers across—is no small feat.
Now, researchers working at the National Institute of Standards and Technology (NIST) in the United States, in collaboration with the universities of Southampton (UK)and Rochester (US), have developed a simple new technique for locating them and used it to create high-performance single photon sources.
This new development, which is published in Nature Communications, may make the manufacture of high-performance photonic devices using quantum dots much more efficient. Such devices are usually made in regular arrays using standard nanofabrication techniques like electron-beam lithography and semiconductor etching.
However because of the random distribution of the dots, only a small percentage of them will line up correctly, at the optimum position within the device. This overall process thus produces very few working devices.
“This is a first step towards providing accurate location information for the manufacture of high performance quantum dot devices,” says NIST physicist Kartik Srinivasan. “So far, the general approach has been statistical - make a lot of devices and end up with a small fraction that work - but our camera-based imaging technique instead seeks to map the location of the quantum dots first, and then uses that knowledge to build optimized light-control devices in the right place.”
Dr Luca Sapienza, from the University’s Quantum Light and Matter group, says: “This new technique is sort of a twist on a red-eye reducing camera flash, where the first flash causes the subject’s pupils to close and the second illuminates the scene.”
In their setup, instead of xenon-powered flash the team used two LEDS. One LED activates the quantum dots when it flashes (you could say this LED gives the quantum dots red eye). At the same time, a second, different color LED flash illuminates metallic orientation marks placed on the surface of the semiconductor wafer the dots are embedded in. Then a sensitive camera snaps a 100-micrometer by 100-micrometer picture.
By cross-referencing the glowing dots with the orientation marks, the researchers can determine the dots’ locations with an uncertainty of less than 30 nanometers. Their coordinates in hand, scientists can then tell the computer-controlled electron beam lithography tool to place any structure the application calls for in its proper relation to the quantum dots, resulting in many more usable devices.
Using this technique, the researchers demonstrated grating-based single photon sources in which they were able to collect 50 per cent of the quantum dot’s emitted photons, the theoretical limit for this type of structure.
They also demonstrated that more than 99 per cent of the light produced from their source came out as single photons. Such high purity is partly due to the fact that the location technique helps the researchers to quickly survey the wafer (10,000 square micrometers at a time) to find regions where the quantum dot density is especially low–only about one per 1,000 square micrometers. This makes it far more likely that each grating device contains one—and only one—quantum dot.
This work was performed in part at NIST’s Center for Nanoscale Science and Technology (CNST), a national user facility available to researchers from industry, academia and government.
Notes for editors:
1. L. Sapienza, M. Davanço, A. Badolato and K. Srinivasan. Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission. Nature Communications, 6, 7833 doi:10.1038/ncomms8833. Published 27 July 2015.
2. The attached image shows circular grating geometry for efficiently extracting single photons from a quantum dot.
3. Through world-leading research and enterprise activities, the University of Southampton connects with businesses to create real-world solutions to global issues. Through its educational offering, it works with partners around the world to offer relevant, flexible education, which trains students for jobs not even thought of. This connectivity is what sets Southampton apart from the rest; we make connections and change the world. http://www.southampton.ac.uk/
For further information:
Glenn Harris, Media Relations, University of Southampton, Tel 023 8059 3212, email G.Harris@soton.ac.uk, Twitter: @glennh75
Follow us on twitter: http://twitter.com/unisouthampton
Like us on Facebook: www.facebook.com/unisouthampton
Steve Williams | newswise
OU-led team discovers rare, newborn tri-star system using ALMA
27.10.2016 | University of Oklahoma
First results of NSTX-U research operations
26.10.2016 | DOE/Princeton Plasma Physics Laboratory
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
27.10.2016 | Materials Sciences
27.10.2016 | Physics and Astronomy
27.10.2016 | Life Sciences